The most common causes of hemorrhoids are straining at bowel movements, prolonged sitting and pregnancy. Internal hemorrhoids occur above the anal sphincter, and external hemorrhoids occur below, outside the anal canal.
Update Date 5/16/2011
Updated by: Todd Eisner, MD, Private practice specializing in Gastroenterology, Boca Raton, FL. Clinical Instructor, Florida Atlantic University School of Medicine. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.